Messages in this thread | | | Date | Wed, 8 Jun 2005 09:38:05 +0530 (IST) | From | Nagendra Singh Tomar <> | Subject | Re: Zeroed pages returned for heap |
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On Tue, 7 Jun 2005, Peter Staubach wrote:
> Nagendra Singh Tomar wrote: > > >Hi all, > > The short version first. > >Is it OK for an application (a C library implementing malloc/calloc is > >also an application) to assume that the pages returned by the OS for heap > >allocation (either directly thru brk() or thru mmap(MAP_ANONYMOUS)) will > >be zero filled. > > > > An application which makes assumptions about the contents of newly allocated > memory would seem to be making very dangerous assumptions.
Thats what glibc does. Ulrich confirmed that. I would say thats not a bad optimization on glibc's part as it does not really make sense to zero out a memory again in user space if we know for sure that new heap memory that kernel hands over to us will be zeroed. I'm not sure though whether this is a documented kernel ABI.
> > Ignoring that, would it not be considered to be a security violation to hand > pieces of memory to applications without erasing the old contents of the > pages?
I understand that for a desktop/server running Linux but not for an embedded box where all the applications that run on the box is controlled by you.
Thanx, Tomar
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